Vacuum countergravity casting apparatus and method

Abstract

Vacuum countergravity casting apparatus and process employ a container having a peripheral wall defining an open bottom chamber that receives one or more molds or destructible patterns. A first inherently unstable mass of particulates (e.g., binderless sand) is disposed in the chamber about the molds/patterns and a second supportive mass of bonded particulates (e.g., resin-bonded sand) is disposed in the chamber about the molds/patterns beneath the first mass. The second supportive mass is strong enough to support the first mass and preferably the molds/patterns as well as castings ultimately formed as necessary during the casting operation in the event of intentional or unexpected interruption of a negative differential pressure established between the inside and outside of the container.

We claim: 
     
       1. Apparatus for countergravity casting of a melt, comprising: a) a container having a peripheral wall defining a chamber having an open bottom end,   b) means disposed in the chamber for forming a mold cavity and melt inlet for communicating the mold cavity with an underlying source of the melt,   c) a first inherently unstable mass of particulates disposed in the chamber about the mold cavity and inlet-forming means, and   d) a second supportive mass of bonded particulates disposed in the container about the mold cavity and inlet-forming means beneath said first mass for supporting said first mass in the chamber as the container and source are relatively moved toward/away from one another for communicating/discommunicating said mold cavity and said source, as appropriate, for casting.   
     
     
       2. The apparatus of claim 1 wherein the first mass comprises substantially binderless sand. 
     
     
       3. The apparatus of claim 1 wherein the second mass comprises resin-bonded sand. 
     
     
       4. The apparatus of claim 1 wherein the second supportive mass supports said first mass and said mold cavity and inlet-forming means as well as castings formed thereby, as necessary, in the container as the container and the source are relatively moved toward/away from one another. 
     
     
       5. The apparatus of claim 4 wherein said second supportive mass is interlocked between said peripheral wall and said mold cavity and inlet-forming means. 
     
     
       6. Apparatus for countergravity casting of a melt, comprising: a) a container having a peripheral wall defining a chamber having an open bottom end,   b) a gas permeable mold disposed in the chamber, said mold including a mold cavity and a melt inlet communicating the mold cavity with an underlying source of the melt,   c) a first inherently unstable mass of particulates disposed about the mold in the chamber, and   d) a second supportive mass of bonded particulates disposed about the mold in the container beneath said first mass for supporting said second mass in the chamber as the container and source are relatively moved toward/away from one another to engage/disengage said melt inlet and said source, as appropriate, for casting.   
     
     
       7. The apparatus of claim 6 wherein the mold comprises a bonded particulate mold. 
     
     
       8. The apparatus of claim 7 wherein the mold comprises a resin-bonded sand mold. 
     
     
       9. The apparatus of claim 6 wherein the first mass comprises substantially binderless sand. 
     
     
       10. The apparatus of claim 6 wherein the second mass comprises resin-bonded sand. 
     
     
       11. The apparatus of claim 10 wherein the resin-bonded sand is cured in-situ in the container. 
     
     
       12. Apparatus for countergravity casting of a melt, comprising: a) a container having a peripheral wall defining a chamber having an open bottom end,   b) a gas permeable mold disposed in the chamber, said mold including a mold cavity and a melt inlet for communicating the mold cavity with an underlying source of the melt,   c) a first inherently unstable mass of particulates disposed about the mold in the chamber remote from said open bottom end, and   d) a second supportive mass of bonded particulates disposed about the mold in the chamber beneath said first mass for supporting said mold and said first mass, as necessary, in the chamber as the container and the source are relatively moved toward/away from one another to engage/disengage said melt inlet and said source for casting.   
     
     
       13. The apparatus of claim 12 wherein the mold comprises a bonded particulate mold. 
     
     
       14. The apparatus of claim 13 wherein the mold comprises a resin-bonded sand mold. 
     
     
       15. The apparatus of claim 12 wherein the first mass comprises substantially binderless sand 
     
     
       16. The apparatus of claim 12 wherein the second mass comprises resin-bonded sand. 
     
     
       17. The apparatus of claim 16 wherein the resin-bonded sand is cured in-situ in the container. 
     
     
       18. The apparatus of claim 12 wherein said peripheral wall includes means for interlocking with said second mass. 
     
     
       19. The apparatus of claim 18 wherein said interlocking means comprises a protuberance on the peripheral wall for engaging said second mass. 
     
     
       20. The apparatus of claim 12 wherein the mold includes means for interlocking with said second mass. 
     
     
       21. The apparatus of claim 20 wherein said interlocking means comprises a recess on the mold wall for receiving said second mass. 
     
     
       22. The apparatus of claim 21 wherein said interlocking means comprises a protuberance on the mold for engaging said second mass. 
     
     
       23. The apparatus of claim 12 further comprising means for establishing a negative differential pressure between the mold cavity and the source when the melt inlet and the source are engaged sufficient to urge the melt upwardly from the source into the mold cavity. 
     
     
       24. A method of countergravity casting a melt, comprising the steps of: a) disposing a container about means for forming a mold cavity and a melt inlet beneath said mold cavity such that an open bottom end of the container is disposed proximate the melt inlet,   b) providing a first inherently unstable mass of particulates about the mold cavity and inlet-forming means in the container,   c) providing a second mass of bonded particulates about the mold cavity and inlet-forming means in the container such that, when the container is oriented to position said melt inlet facing the underlying source of the melt, said first mass is disposed atop said second mass and is supported in the container by said second mass,   d) relatively moving the container and the source to engage said melt inlet and said source, and   e) drawing the melt upwardly toward the melt inlet into the mold cavity when said melt inlet and said source are engaged.   
     
     
       25. The method of claim 24 wherein in step e), a negative differential pressure is established between the mold cavity and the source when said melt inlet and said source are engaged to draw the melt upwardly into the mold cavity. 
     
     
       26. A method of countergravity casting a melt, comprising the steps of: a) positioning a gas permeable casting mold in a container having an open end, said mold having a mold cavity and a melt inlet for communicating said mold cavity with an underlying source of the melt,   b) providing a first inherently unstable mass of particulates about the mold in the container,   c) providing a second mass of bonded particulates about the mold in the container such that, when the container is oriented to position said melt inlet facing the underlying source of the melt, said first mass is disposed atop said second mass and, as necessary, said second mass supports said first mass in the container,   d) relatively moving the container and the source to engage said melt inlet and said source, and   e) drawing the melt upwardly through the melt inlet into the mold cavity when said melt inlet and said source are engaged.   
     
     
       27. The method of claim 26 wherein the second mass is bonded in-situ in the container about the mold. 
     
     
       28. The method of claim 27 wherein said second mass is bonded in-situ in the container by disposing a binder/particulates mixture comprising said second mass in the container about the mold proximate said open end and setting/curing the binder after said first mass is disposed in the container to bond the particulates of said mixture. 
     
     
       29. The method of claim 28 wherein the second mass is formed of resin-bonded sand. 
     
     
       30. The method of claim 26 wherein in step e), a negative differential pressure is established between the mold cavity and the source when said melt inlet and said source are engaged to draw the melt upwardly into the mold cavity. 
     
     
       31. The method of claim 26 wherein the second supportive mass supports the first mass and the mold in the container during step (d). 
     
     
       32. The method of claim 31 further including relatively moving the container and the source to disengage said melt inlet from said source after filling the mold cavity with said melt, including supporting the melt-filled mold and the first mass of particulates in the container by said second mass of bonded particulates. 
     
     
       33. The method of claim 26 including interlocking said second mass and said container. 
     
     
       34. The method of claim 33 including interlocking said second mass and said mold. 
     
     
       35. A method of countergravity casting a melt, comprising the steps of: a) positioning a gas permeable, bonded particulate casting mold in a container proximate an open bottom end thereof, said mold having a mold cavity and a melt inlet disposed proximate said open bottom end for communicating said mold cavity to an underlying source of the melt,   b) forming a first mass of substantially binderless particulates in the container about the mold remote from said open bottom end,   c) forming a second supportive mass of bonded particulates in the container about the mold beneath said first mass proximate said open bottom end, including interlocking said second mass between said container and said mold, whereby said second mass supports said mold and said first mass in said container,   d) relatively moving the container and the source to engage the melt inlet and the source, and   e) establishing a negative differential pressure between the mold cavity and the source when said melt inlet and said source are engaged sufficient to urge the melt upwardly through said melt inlet into said mold cavity.